Homologous series of aromatic and heterocyclic hydrocarbons occur in varying proportions in crude oils and their refined products, depending on the source of the oil and the refining process applied. These aromatic hydrocarbons and heterocycles adversely affect several stages of petroleum production, handling, and processing. Aromatic compounds influence the persistence and toxicity of oils spilled in the environment and has poor combustion characteristics in diesel engines, including low cetane number and high particulate matter (soot) formation. During refining, nitrogen heterocycles (e.g., carbazoles) inactivate chemical catalysts, interfere with catalytic hydrodesulfurization and consume large amounts of H2. As well, combustion of fuels containing S and N heteroatoms produces SOx and NOx in emissions implicated in acid rain.
Effective and cost-efficient reduction of aromatic hydrocarbons and heterocycles in crude oils and fuels therefore is desirable from an environmental viewpoint and is of interest to the refining industry.
Several chemical process have been used till date in the prior art to reduce the undesirable aromatic and heterocyclic compounds from crude oils and fuels.
U.S. Pat. No. 6,160,193 describes a two-step process for the removal of sulfur and nitrogen containing compounds from petroleum distillates. The first step of the process is to oxidize the sulfur-containing compounds of the fuel. The oxidization process converts sulfur compounds to highly polar sulfones. Nitrogen compounds are likewise converted to polar oxidized species. An example of an oxidizing agent that can be successfully used in this process is peroxysulfuric acid, often called Caro's acid. Oxidations are typically carried out at about 30 to 100° C., and preferably at 60 to 95° C. Low pressures are used, typically less than about 150 psig (pounds per square inch, gauge), and preferably less than about 30 psig, the autogenous pressures created by the vapors of the fuel and the various reactants and solvents. Sulfur- and nitrogen-containing compounds are oxidized using a selective oxidant to create compounds that can be preferentially extracted from a petroleum distillate due to their increased relative polarity. The second step of the process uses a solvent to extract the sulfones from the fuel oil.
U.S. Pat. No. 5,958,224 relates to a process for removing hard sulfurs from hydrocarbon streams by selectively oxidizing hard sulfurs in a hydrotreated stream are oxidized into the corresponding sulfoxides and sulfones, under oxidizing conditions in the presence of an effective amount of an oxidizing agent, wherein the oxidizing agent is a peroxometal complex and wherein the hard sulfurs. The said oxidizing agent is a peroxometal complex selected from the group consisting of one of the following forms: LMO (O2)2, (LL′) MO (O2)2, LMO(O2).2.H2O, and mixtures thereof, wherein M is selected from the group consisting of Mo, W, Cr and mixtures thereof and wherein L and L′ are neutral legends and wherein said sterically hindered sulfurs are converted into oxidation products.
However, the aforesaid and other thermochemical processes require high temperature; high-pressure catalytic hydrogenation to saturate and break the aromatic rings. These are not practical considering the problems posed by them including unfavorable reaction kinetics, high consumption of thermal energy and hydrogen (which contributes to greenhouse gases and other emissions), and production of less desirable side-products such as gaseous hydrocarbons through non-specific reactions.
The foregoing limitations to conventional desulfurization, denitrogenation and dearomatization process such as oxidations using chemical oxidants have spurred considerable and longstanding interest among those engaged in the extraction and refining of fossil fuels in developing commercially viable techniques of biocatalytic upgrading. Biocatalytic upgrading is as the harnessing of metabolic processes of suitable bacteria to the upgrading of fossil fuels. Biocatalytic upgrading typically involves mild (e.g., ambient) conditions, and does not involve the extremes of temperature and pressure required for HDS.
Various biocatalytic process for reduction of aromatic and heterocyclic hydrocarbons have been disclosed in the prior art.
U.S. Pat. No. 5,510,265 relates to a process for the deep desulfurization of a liquid fossil fuel containing organic sulfur comprising aromatic sulfur-bearing heterocycles, wherein the fossil fuel is (a) subjected to hydrodesulfurization or microbial desulfurization, (b) contacted with a biocatalyst in an aqueous medium in an amount and under conditions sufficient for the conversion of aromatic sulfur-bearing heterocycles to inorganic sulfur, wherein the biocatalyst comprises bacteria or a substantially cell-free preparation thereof having the capability of the parent microorganism for catalyzing the removal of sulfur from aromatic sulfur-bearing heterocycles, thereby preparing a deeply desulfurized fossil fuel; and (c) separated from the aqueous medium.
U.S. Pat. No. 5,910,440 discloses a process to remove organic sulfur from organic compounds and organic carbonaceous fuel substrates containing sulfur compounds having sulfur-carbon bonds. The steps of the process include oxidizing the sulfur species to the sulfone and/or sulfoxide form, and reacting the sulfone and/or sulfoxide form in an aqueous media of the reacting step, including a hydride transfer reducing agent. In a particular embodiment, the reducing agent is sodium formate, the oxidizing agent is a microorganism as exemplified by Rhodococcus species ATCC 55309 or Rhodococcus species ATCC 55310 or combinations thereof.
U.S. Pat. No. 5,985,650 describes a process for enhancing the rate of desulfurizing a fossil fuel containing organic sulfur compounds, comprising the steps of: a) contacting the fossil fuel with an aqueous phase containing a biocatalyst capable of cleaving carbon-sulfur bonds and a rate-enhancing amount of a flavoprotein, thereby forming a fossil fuel and aqueous phase mixture; b) maintaining the mixture of step (a) under conditions sufficient for cleavage of the carbon-sulfur bonds of the organic sulfur molecules by the biocatalyst, thereby resulting in a fossil fuel having a reduced organic sulfur content; and c) separating the fossil fuel having a reduced organic sulfur content from the resulting aqueous phase.
U.S. Pat. No. 6,071,738 relates to a process for the desulfurization of a fossil fuel containing one or more organosulfur compounds. This process comprises the steps of (1) contacting the fossil fuel with a biocatalyst capable of converting the organosulfur compound to an oxyorganosulfur compound which is separable from the fossil fuel; and (2) separating the oxyorganosulfur compound from the fossil fuel. Biocatalytic enzyme preparations that are useful in the present invention include microbial lysates, extracts, fractions, subfractions, or purified products obtained by conventional means and capable of carrying out the desired biocatalytic function. Generally, such enzyme preparations are substantially free of intact microbial cells, i.e., the enzyme preparations are cell-free fractions.
Ayala et al. 1998 (Ayala M, Tinoco R, Hernandez V, Bremauntz P, Vazquez-Duhalt (1998) Biocatalytic oxidation of fuel as an alternative to biodesulfurization. Fuel Processing Technology 57:101-111.) has described a bioxidative process for fuel desulfurization using enzyme chloroperoxidase from Caldariomyces fumago. The process includes the steps of biocatalytic oxidation of organosulfides and thiophenes, contained in the fuel, with hemoproteins to form sulfoxides and sulfones, followed by a distillation step in which these oxidized compounds are removed from the fuel. In this process straight-run diesel fuel containing 1.6% sulfur was biocatalytically oxidized with chloroperoxidase from Caldariomyces fumago in the presence of 0.25 mM hydrogen peroxide. The reaction was carried out at room temperature and the organosulfur compounds were effectively transformed to their respective sulfoxides and sulfones which were then removed by distillation. The resulting fraction after distillation contained only 0.27% sulfur. They have proposed biocatalytic oxidation of fuels as an interesting alternative to whole cell biodesulfurization.
Wu et al. (2002) (Q. Wu, M. R. Gray, M. A. Pickard, P. M. Fedorak, J. M. Foght 2002 Petroleum Chemistry Division Preprints 47(1) 615061) described biocatalytic ring opening of heterocycles dissolved in crude oil using bacterium Pseudomonas fluoresencens strain LP6a.
U.S. Pat. No. 7,101,410 relates to a microbiological process of desulfurization (MDS) of hydrocarbon fuels such as coal, coal tar and petroleum uses an aqueous microbial biocatalytic agent which is not significantly reproducing but is still capable of oxidizing inorganic sulfur compounds and/or of selectively cleaving sulfur-carbon bonds in organic compounds, thereby removing sulfur with insignificant losses in fuel value. Microorganisms are selected according to the type of fuel sulfur present and the environment in which the desulfurizing process is to take place. One embodiment allows droplets of highly concentrated cell-water suspensions to pass from the top surface of the fuel through to the bottom, desulfurizing along the way and removing the sulfur products of the process as well.
U.S. Pat. No. 6,461,859 relates to a process of removing thiophenic and organosulfide compounds from a fossil fuel comprising the steps of contacting the fossil fuel with hemoproteins, which oxidize the sulfur containing compounds to sulfoxides and sulfones in a reaction system containing organic solvent or not, and followed by a distillation step in which sulfoxides and sulfones are removed from the fuel. Preferred biocatalysts include hemoproteins such as chloroperoxidase from Caldariomyces fumago, and peroxidases and cytochromes from animal, plant or microbial cells. The hemoprotein biocatalyst can be contacted with the fossil fuel in free or immobilized forms. The reaction can be carried out in the presence of the fuel alone or with addition of any organic solvent. The biocatalytically oxidized fuel is then distilled in order to eliminate the heavy fraction which contains most of oxidized organosulfur compounds. The light distillate contains significantly lower concentrations of sulfur when compared with the starting fossil fuel.
U.S. Pat. No. 6,071,738 relates to a process for the desulfurization of a fossil fuel containing one or more organosulfur compounds. In one embodiment, the process comprises the steps of (1) contacting the fossil fuel with a biocatalyst capable of converting the organosulfur compound to an oxyorganosulfur compound which is separable from the fossil fuel; and (2) separating the oxyorganosulfur compound from the fossil fuel. The oxyorganosulfur compound can then be isolated, discarded or further processed, for example, via desulfurization by a biocatalyzed process or an abiotic process, such as hydrodesulfurization.
U.S. Pat. No. 6,943,006 relates to a process for selective cleavage of C—N bonds genes that encode for at least one enzyme suitable for conversion of carbazole to 2-aminobiphenyl-2,3-diol are combined with a gene encoding an amidase suitable for selectively cleaving a C—N bond in 2-aminobiphenyl-2,3-diol, forming an operon that encodes for cleavage of both C—N bonds of said carbazole. The operon is inserted into a host culture which, in turn, is contacted with the carbazole, resulting in selective cleavage of both C—N bonds of the carbazole. Also disclosed is a new microorganism that expresses a carbazole degradation trait constitutively and a process for degrading carbazole employing this microorganism.
U.S. Pat. No. 6,124,130 relates to a process for removal of sulfur from fossil fuels containing sulfur by incubation of the fuel with microbes isolated and purified from soil or water that selectively extract the sulfur without apparently utilizing the fuel as a carbon or energy source. Preferred biodesulfurization microbes remove at least about 20% of the sulfur. The microbes are obtained in a multi-step screen that first selects microorganisms that utilize dibenzothiophene (DBT) as a sole source of sulfur, and then tests these in incubations with fossil fuels; organisms that desulfurize DBT without metabolizing the DBT phenyl ring structures and desulfurize fuels only when a second carbon source devoid of sulfur is present are identified and employed in desulfurization processes. Two cultures, CDT-4 and CDT-4-b, were particularly efficacious in the desulfurization of liquid fossil fuels.
U.S. Pat. No. 6,071,738 relates to a process for the desulfurization of a fossil fuel containing one or more organosulfur compounds. In one embodiment, the process comprises the steps of (1) contacting the fossil fuel with a biocatalyst capable of converting the organosulfur compound to an oxyorganosulfur compound which is separable from the fossil fuel; and (2) separating the oxyorganosulfur compound from the fossil fuel. The oxyorganosulfur compound can then be isolated, discarded or further processed, for example, via desulfurization by a biocatalyzed process or an abiotic process, such as hydrodesulfurization.
US 20030170874 relates to process for treating liquid hydrocarbon, includes the steps of providing a liquid hydrocarbon containing complex sulfur-containing compounds, providing a bioactive material selected from or derived from members of genus Alcaligenes; and exposing the liquid hydrocarbon to the bioactive material under effective conditions such that the bioactive material interacts with the complex sulfur compounds and transforms the organic sulfur-containing compounds into inorganic sulfur compounds.
Further, several microbes are known to have activity against PAH and heterocycles especially aromatic ring opening and hydroxylation activity. U.S. Pat. No. 6,221,651 discusses a mutant Pseudomonas ayucida strain ATCC PTA-806 which is able to selectively cleave organic C—N bonds and reduce the nitrogen content of organic carbonaceous materials.
Considering the aforesaid prior arts, wherein the process involves numerous steps and are uneconomical even, it is desirable to provide a process capable of removing sulfur, nitrogen and reducing aromatics in one step from hydrocarbon fuels, which could be implemented without complex and costly equipment or the use of expensive or hazardous chemicals. Further, economic analyses indicate that one limitation in the commercialization of the technology is improving the reaction rates and specific activities of the biocatalysts, such as the bacteria and enzymes that are involved in the desulfurization reactions. Yet no microorganism is wild or genetically modified which can meet the activity required for commercial utilization of the process. Moreover, none of the biocatalyst is known which can attack on both organ sulfur compounds and organonitrogen compounds and reduce total aromatic content as well.
It is especially desirable if these criteria could be met to produce a fuel, which could be burnt without requiring the aqueous phase be removed prior to combustion. This need grows progressively more urgent as lower-grade, higher-sulfur fossil fuels are increasingly being used, while concurrently the sulfur emission standards set up by the regulatory authorities have become ever more stringent.
Therefore, there is a need to improve upon the limitations in the prior art. In view of the above the present invention provides an improved process for upgrading crude oil and liquid fuel by reducing aromatic, sulfur and nitrogen contents.